This invention relates to wheels for vehicles such as bicycles and wheelchairs, and, in particular, to hubless wheels designed to lessen the weight and improve the aerodynamics of the vehicle.
Speed sport athletes such as cyclists continue to seek bicycle equipment improvements which gain them an advantage in racing competitions. Bicycle wheels are one type of equipment specifically targeted for improvement, as designers attempt to develop wheels with improved weight and aerodynamic characteristics relative to existing bicycle wheels. Previous wheel enhancements which decrease wheel weight have been accomplished by modifying the materials of wheel construction. For instance, heavy metal wheel rims of the past have been replaced with lower weight, high strength composites. These composites are typically carbon fiber composite shells having filled, lightweight cores constructed from, for instance, various foam materials, balsa wood, or NOMEX.TM..
While altering the materials of construction has achieved lower wheel weights, standard wheel designs continue to suffer from a major shortcoming. Specifically, the wheel hub and its associated spokes and bicycle frame tripletree detrimentally affect both the aerodynamic and weight characteristics of the wheel. Standard wheels include a central hub, disposed at the wheel's axis of rolling rotation, with numerous connected spokes extending radially therefrom to connect with the tire supporting wheel rim. Even wheels wherein the spokes have been replaced with a solid disc for aerodynamic purposes still employ a hub. The central hub is then connected to the remainder of the bicycle via the bicycle frame tripletree, i.e. the tubular component which at its upward end is a single tube, operatively connected to the handlebars, and at its lower end includes a tubular forked extension which fits over the sides of the wheel and connects with both axial sides of the hub. The spokes, hub and forked extension of the tripletree add weight to the bicycle which if avoided would make the bicycle desirably lighter. In addition, the spokes, hub and particularly the forked extension of the tripletree hinder the aerodynamics of the bicycle as they frequently axially project beyond the forward profile of the wheel, i.e. the tire axial thickness. Consequently, these pieces of equipment encounter passing air during operation and generate undesirable drag on the bicycle.
In addition to increasing wheel weight and thereby vehicle weight, spokes can be hazardous to persons including the vehicle operator. For instance, when a person is riding a bicycle, rigid materials such as sticks which inadvertently are introduced between into the spokes and the tripletree forked extension can bind the wheel, thereby throwing the rider and subjecting her to injury. Moreover, a person can be seriously injured if her hand is accidentally inserted into the rapidly rotating spokes of a wheel on a wheelchair or a bicycle.
Previous attempted designs for hubless, spokeless wheels for bicycles, such as those disclosed in U.S. Pat. Nos. 4,045,096 and 3,329,444, may be operational but are nonetheless undesirable from a standpoint of optimizing vehicle weight or aerodynamics. Because these designs involve shrouds or frame members which partially encapsulate a significant portion of the ground engaging tread, their forward profile is wider than the tread for much of the height of the wheel and consequently increased drag is present. In addition, the multiplicity of fasteners involved in the assembly of the shrouds and the multiplicity of bearings taught employed add unnecessary weight which is desirable to be reduced.
U.S. Pat. No. 5,071,196 discloses hubless spokeless wheels for motor vehicles apparently having annular bearing means which extend around the entire circumference of the wheel on both its stationary and rotating components. While such a bearing design may be advantageous from a standpoint of fully minimizing friction, and may in fact be necessary in applications where significant weights are being carried, introducing excess bearings in situations such as bicycle racing competitions where minimizing weight is of heightened importance may be counterproductive. In other words, reducing friction by an additional fractional amount by increasing the number of bearings does not merit the concomitant relatively significant increase in weight.